Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR CONSTRUCTION OF RIGID PHOTOVOLTAIC MODULES
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority of U.S. Provisional Patent
Application
No. 60/576,626 filed June 4, 2004, which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates generally to photovoltaic cells and modules
thereof,
such as solar cells and solar cell modules. More particularly, the present
invention relates
to structural stiffening of solar modules through geometric shaping, including
corrugation.
BACKGROUND OF THE INVENTION
Solar modules for generating electricity are well known in the art. The most
common solar modules employ a glass superstrate that provides rigidity to the
module,
but also greatly increases the mass of the module and makes transportation
difficult. To
create a large solar module, the thickness of the glass is increased to
provide sufficient
strength to ensure the integrity of the module. If the glass is too thin, and
does not
provide sufficient rigidity, it can crack and the module will be useless.
Conventional photovoltaic modules can produce 200W (with a surface area of
approximately two square meters), but at such capacity their weight approaches
50
pounds. This weight limits the utility of these laminates for use in products
that require
simplified installation. This weight is mainly due to the requirement for
thicker glass as
surface area increases, in order to meet wind load requirements. Thinner glass
is more
susceptible to being fractured and is also susceptible to shear and torsion. A
small
fracture in the glass of a conventional solar module effectively renders the
module
useless, as the glass is typically safety glass and a small fracture will
result in the rapid
fracturing of the entire module. One skilled in the art will appreciate that
substituting
another material for glass in a conventional solar module is undesirable due
to the
characteristics of other transparent media.
Flexible solar modules are known in the field. These modules typically make
use
of thin film cells or cells using spherical silicon elements as the
photovoltaic element, and
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are bonded between flexible superstrates and substrates by an encapsulant.
These solar
modules are, by their very nature, lighter weight than the conventional glass
modules, but
offer no support and cannot bear a load.
Flexible solar modules can typically be manufactured at a lower cost than
glass
photovoltaic (PV) modules and offer many benefits related to portability and
durability but
cannot be incorporated as structural elements in construction as they cannot
support a
load.
By making flexible modules more rigid, they could be incorporated as
structural
elements in place of glass PV modules. This would allow a reduction in weight
and
0 allows for better scalability, as the mass per watt of generating capacity
would not
necessarily need to increase as it does with glass modules. Although using
multiple
smaller glass modules can often overcome the increase in the mass per watt, it
increases
the number of connections needed and amount of cable, which increases the
overall cost
and results in a more complex installation process.
5 Large glass PV modules also cause installation difficulties as the PV module
adds
to the weight of any pre-assembled component and thus requires heavy machinery
to
hoist modules onto roofs.
A mechanism to incorporate a rigid structure into flexible PV modules would
address many of the downfalls of glass PV modules including the fragile nature
of the
?0 modules, the increased weight due to the thick glass, and the added
installation
difficulties.
Numerous pieces of prior art have been directed to creating standard roofing
elements with integrated solar modules. A discussion of a sampling of the art
is provided
below.
?5 U.S. Patent No. 5,935,343 to Hollick teaches affixing solar cells to the
top of a
corrugate. The cells are illustrated as being bolted to the top surface of the
corrugate or
affixed across the openings in the top surface. Hollick uses this
configuration to allow air
flow beneath the module to promote cooling. Hollick's teachings do not result
in an
integral unit, and would thus be difficult to implement using flexible
modules, as the areas
30 of the module not supported by the corrugate would not adequately bear wind
loads.
Above all, Hollick does not teach a method for constructing a stand alone
module which
can be rack mounted.
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U.S. Patent No. 6,201,179 to Dalacu discloses an array of modules installed on
an
interlocking corrugated support. The Dalacu reference also describes attaching
modules
to an interlocking corrugated roofing bed, using techniques similar to those
taught by
Hollick. As a result, the system taught in the Dalacu reference does not
result in a stand
alone module which can be rack mounted and in which system modules can be
added or
removed with ease.
U.S. Patent No. 5,338,369 to Rawlings discloses an extruded corrugated core PV
panel. The Rawlings reference describes an interlocking array of modules for
use as an
integrated roofing system. Though this system provides some structural
integrity for the
0 module, it requires the panels to be installed in an interlocking fashion,
which can
complicate installation and replacement of the modules. Additionally, as shown
in Figure
2, the modules are individually wired together at a combiner box, which is
more
complicated than simple inter-module connections. This adds to the
installation
complexity and cost.
5 U.S. Patent No. 5,505,788 to Dinwoodie discloses a corrugated pan to hold
phase
change material against modules. As illustrated in the Dinwoodie reference,
modules are
simply affixed to the top of a corrugate or other structure, as a means of
attachment to a
horizontal surface. As a result, this approach would be required to use stand
alone
modules which have passed wind load requirements prior to attachment to said
mounting
?0 structure.
U.S. Patent No. 5,092,939 to Nath discloses PV cells laminated on a metal coil
for
field forming to make a standing seam roof construction. Significant shading
of areas of
the modules is likely on a seasonal basis, as the seams stand above the solar
cell plane,
creating reliability issues. Ease of replacement for individual modules is
quite
?5 questionable for a system of this design.
U.S. Patent No. 5,232,518 to Nath et al. discloses a roofing system similar to
that
disclosed in the '939 patent. The '518 patent teaches the interconnection of
all installed
modules so that a single connection to the module array is utilized. As noted
above,
shading and ease of module replacement are major issues with such designs.
30 U.S. Patent No. 4,433,200 to Jester et al, discloses a roll formed pan on
which
conventional fragile silicon wafer-based cells are mounted. Without any
internal
reinforcement in this design, simply a frame around the perimeter, this
approach fails to
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provide any improvement over glass superstrate designs as weight per area must
significantly increase as module size increases, since much thicker substrates
will be
required to sustain wind load requirements. As a result, the approach taught
by Jester is
not suitable for large area modules.
U.S. Patent No. 6,606,830 to Nagao et al is directed to reducing the number of
connections to a house that a solar array requires. As disclosed in the Nagao
reference,
the PV modules are interlocking and they form a serial connection to each
other. As
such, individual modules are not easily replaced and also cannot withstand
wind load
requirements without first attachment to a roof deck.
0 U.S. Patent Application Publication No. 2002/0112419 to Dorr et al. is
directed to
affixing PV modules to a corrugate by use of an adhesive, and draws connecting
cables
from each individual module. That the specified corrugate structure is filled
with
insulating foam is a significant problem as inadequate dissipation of heat
severely limits
device performance. Additionally, this design suffers from shading by
corrugate elements
above the plane of the attached modules.
U.S. Patent No. 6,498,289 to Mori et al. teaches a roofing element having a PV
cell. A PV cell is attached to a backing whose sides are then bent into
flanges. Elements
are then added to the backing to space the structure from the roof. These
spacers are
then affixed to the roof, allowing for air ventilation behind the panel.
Though bending the
?0 edges of the backing and affixing spacers provides support to the flexible
PV panel, Mori
admits that the panels cannot bear loads as the areas between spacers are not
supported and thus can bend under loads.
One skilled in the art will appreciate that the interconnection of the solar
modules
as taught by many prior art references results in a large solar array that is
physically
interlocked. Should one of the modules fail most of this prior art does not
provide for
ease of replacement or removal from the circuit, to circumvent performance and
reliability
issues.
It is, therefore, desirable to provide a supporting structure for flexible
solar
modules that provides rigidity and strength to allow the flexible solar module
to bear loads
for a variety of installation methods. It is also desirable to provide a
modular structural
element having a flexible solar panel capable of being removed or replaced
with relative
ease.
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SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at least one
disadvantage of previous photovoltaic panel structured elements.
In a first aspect of the present invention there is provided a rigid solar
module
having a flexible solar module prelaminate. The module comprises a metal
backing, a
corrugated backing and a junction box. The metal backing is affixed to the
prelaminate.
Preferably, this provides a degree of rigidity to the prelaminate. The
corrugated backing
is affixed to the metal backing to provide rigidity to the combination of the
metal backing
and the prelaminate. The junction box is connected to the prelaminate, for
transferring
0 power to a load.
In an embodiment of the present invention, the metal backing is laminated to
the
prelaminate, and its edges are preferably folded over the edges of the
corrugate backing
to affix the corrugate backing to the metal backing. In another embodiment, a
flexible
backing is interposed between the metal backing and the prelaminate in a
laminate. In a
further embodiment, the corrugated backing and the metal backing are integral.
In
another embodiment, the edges of the corrugated backing are folded over the
edges of
the prelaminate to affix the corrugated backing to the metal backing. In a
further
embodiment, the junction box is positioned inside a trough in the corrugate.
In a second aspect of the present invention, there is provided a method of
forming
?0 a rigid photovoltaic module from a flexible photovoltaic module. The method
comprises
the steps of affixing the flexible photovoltaic module to a rigid backing and
structuring the
rigid backed photovoltaic module to provide increased strength in at least one
direction.
In embodiments of the second aspect of the present invention, the rigid
backing is
a metal backing, such as an aluminum backing. In another embodiment, the step
of
affixing can include at least one of gluing the flexible module to the
backing, laminating
the flexible photovoltaic module to the rigid backing, and integrally affixing
the module to
the backing.
In another embodiment, the step of structuring the metal backing includes
bending
the rigid backed photovoltaic module to create a curve. This embodiment
preferably
includes adding supports in a hollow portion of the curve, connecting a
junction box to the
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photovoltaic module and locating the junction box between supports in the
hollow portion
of the curve.
In a further embodiment, the step of structuring the metal backing includes
corrugating the rigid backed photovoltaic module and affixing a junction box
under a flat
section of the corrugated rigid backed photovoltaic module.
In another embodiment, the step of structuring includes affixing the rigid
backed
photovoltaic module to a corrugate. This embodiment preferably includes
folding the
edges of one of the corrugate and the photovoltaic module over the edges of
the other
one of the corrugate and the photovoltaic module, connecting a junction box to
the
0 photovoltaic module and locating the junction box in a trough of the
corrugate.
In a further embodiment, the step of structuring the metal backing includes
bending the rigid backed photovoltaic module to create standing seams beneath
the
plane of the flexible photovoltaic module. This embodiment preferably includes
connecting a junction box to the photovoltaic module and locating the junction
box
5 between two of the standing seams.
Other aspects and features of the present invention will become apparent to
those
ordinarily skilled in the art, upon review of the following description of
specific
embodiments of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
?0 Embodiments of the present invention will now be described, by way of
example
only, with reference to the attached Figures, wherein:
Fig. 1 is a block diagram of a section of a flexible PV prelaminate of the
present invention;
Fig. 2 is a block diagram of a section of a flexible PV cell of the present
?5 invention;
Fig. 3 is a block diagram of a section of a PV module of the present
invention prior to being corrugated;
Fig. 4 is a block diagram of an open corrugated section of the PV module
of Figure 3;
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Fig. 5 is a block diagram of an closed corrugated section of the PV module
of Figure 3;
Fig. 6 is a perspective view of a rigid PV module of the present invention
attached to a corrugated backing;
Fig. 7 is a perspective view of the bottom of the assembly of figure 6;
Fig. 8 is a perspective view of a rigid PV module of the present invention
formed to a curve;
Fig. 9 is a perspective view of the bottom of the assembly of figure 8;
Fig. 10 is a perspective view of corrugated backed modules of the present
0 invention nesting;
Fig. 11 is a perspective view of an embodiment of the present invention;
Fig. 12 is a perspective view of a detail of the embodiment of Figure 11;
Fig. 13 is a flowchart illustrating a method of the present invention;
Fig. 14 is a flowchart illustrating an embodiment of the method of figure 11;
5 Fig. 15 is a flowchart illustrating an embodiment of the method of figure
11;
and
Fig. 16 is a flowchart illustrating an embodiment of the method of figure 11.
DETAILED DESCRIPTION
Generally, the present invention provides a method and system for simplified
?0 installation of affordable and low weight photovoltaic (PV) modules that
can be prepared
in advance for modular installation. PV modules of the present invention use
lower cost
flexible laminates but can serve as replacements to conventional glass modules
as they
are rigid and have a planar surface much as glass PV modules do.
The present invention provides a flexible solar module that has sufficient
structure
25 and rigidity to be used in place of conventional glass superstrate
photovoltaic (PV)
modules. The flexible solar module can use either thin film PV cell-based
panels or
spherical silicon element-based panels. Those skilled in the art will
appreciate the
operation, manufacture and characteristics of these cells.
By eliminating the glass in conventional PV modules, it is possible to build
30 products with areas of more than four square meters that do not exceed 50
pounds in
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weight. This allows for a reduction in overall production costs, as fewer
parts have to be
finished to produce the same equivalent energy. It also allows for a reduction
in
installation costs as fewer parts need to be installed. It is possible to
install lighter
modules using fewer construction workers and overhead cranes are not
necessary.
Although these designs are particularly useful for flexible PV modules, some
of the
designs disclosed below can be used with standard wafer technology when the
backing
designs have adequate rigidity to prevent cell breakage.
Most crystalline silicon wafer PV technologies use a glass superstrate and
aluminum frame with a polymer backing film to encapsulate the solar cells,
providing the
0 needed moisture barrier and structural strength for stand alone modules.
Flexible
modules allow elimination of the weight of the glass cover by replacing it
with a polymer
film such as Ethylene/Tetrafluoroethylene Copolymer (ETFE). Although this
eliminates
the excessive weight of the glass, it is often necessary to provide a
structural backing to
support this flexible sandwich. Many materials that are used for building
construction,
truck trailer construction, and even signage are designed to be lightweight
yet resist wind
loading and uplift forces. The challenge is to find materials that are lighter
than glass but
do not significantly increase production costs. A number of designs which
appear to meet
these requirements have been found and their configuration as well as methods
for
construction will be detailed below as they apply to the present invention.
?0 Typically a flexible solar module is composed of an array of cells. As
illustrated in
Figure 1, each cell 100 is a sandwich of layers. A superstrate 102, typically
ETFE, serves
to protect a layer 104 of PV elements that function as PV diodes. This is the
layer 104
that generates the electrical potential, it can be composed of silicon beads
or a thin film of
silicon or other semiconductor materials. The PV diode, or diodes, is
typically encased in
an encapsulent 106 that bonds the elements to the superstrate 102. As a
product, at this
point, the cell assembly can be referred to as a prelaminate as it has not yet
been affixed
to a substrate, but can be used to generate power.
The prelaminate can be affixed to a substrate 108 such as a film or fiber
backing,
as shown in Figure 2. This can then be affixed to a metal backing 110. The
metal
backing 110 is preferably included with the superstrate 102, the encapsulants
106 and
the substrate 108 in a single step lamination process. In an alternate
embodiment, a
laminate is formed without the metal layer 110 and is then affixed to the
metal layer 110.
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Contacts (not shown) from each cell 100 are connected to the other cells in
the laminate
as is common.
After creating an integral PV laminate on a backing, such as metal layer 110,
the
backing can then be given a structural form. The structural forming can
include
corrugating the backing to create either an open or a closed corrugate.
In the embodiment of an open corrugate, as shown in Figures 3 and 4, the solar
cells 100 can be spaced on the module 112 so that only the flat portions 114
of the
corrugate structure 116 have PV elements 104. The corrugations preferably
remain
below the cell plane to preclude shading and the associated performance and
reliability
0 issues it creates.
In other embodiments, a flexible solar sheet can be attached to the surface of
a
corrugate structure. The lamination of the solar sheet can be performed either
before or
after attachment of a corrugate structure. The corrugate structure can consist
of open
corrugations, as shown in Figure 4, in which troughs 118 are left between rows
of cells
5 100, or it can consist of closed corrugations, as shown in Figure 5, in
which the top
surface 120 of the corrugate 122 becomes a continuous plane. The closed
troughs 124 in
the sheet can be tubuiar, triangular or other standard forms, where the
corrugations 124
are pinched off at their top surface to create a plane. In another embodiment,
a mix of
open and closed corrugations can be formed in either regular or irregular
shapes.
?0 One approach of forming these corrugations is very much like a standing
seam
roof in which pinched-off areas of the sheet are pressed completely flat and
have little
cross-sectional open area, but extend below rather than above the cell plane.
This
embodiment will be discussed below with relation to a figure. Another
variation of this
approach is to simply laminate PV modules to narrow strips of metal (approx.
18-24"
25 wide) and roll the edges in a standard seam roof coil converter. These
pieces can then be
assembled together using conventional assembly hardware or other such standard
means to provide a structurally rigid module having a large surface area, but
again the
edges are formed below rather than above the cell plane. In many of these
embodiments,
a frame is preferably formed at the edges of the sheet to allow for simplified
installation of
30 the modules into a structural framework. End caps may also be placed on the
assembly
to create a complete frame and control air flow.
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Many other embodiments preferably include at least one additional sheet of
material for the additional structural support. This additional support can be
provided by
attaching a flat solar sheet to an existing corrugate or even an extruded
three-
dimensional sheet. The structure preferably provides a planar face of PV cells
though the
face can be either interrupted, as shown with the open corrugate, or curved to
fit a
structured form.
One such design, as illustrated in Figures 6 and 7, invoives attaching a sheet
of
corrugated metal 126 to the back of a PV laminate 128 which has as part of its
construction a metal layer and a plurality of PV cells 100. This attaching can
be done
0 using any one of, or a combination of, screws, rivets, tabs, glue, adhesive
tapes, and
other conventional means. This structure has excellent strength along the
direction of the
rolled corrugation but can be bent to conform to the curvature of a building
surface in the
other direction. Junction boxes 130 can be used to connect the module to other
modules
or to the power system. Preferably the cables 132 are quick connect cables
that allow for
5 rapid installation without requiring sophisticated installation teams. This
structure allows
airflow 134 to aid in the dissipation of heat as air is drawn through the
corrugations.
In another embodiment, a flexible sheet with a metal layer backing is curved
or
bent to fit with a structured form that supports the new shape. Figures 8 and
9 provide
top and bottom perspective views of one such embodiment. A flexible PV module
113
?0 having cells 100 is formed with a rigid back that provides both strength
and rigidity. The
module is then bent to take a shape, such as the illustrated curve. This bent
module can
be attached to structural supports 136. Supports 136 serve to further
reinforce the
structure and provide rigidity. The spaces 138 between supports 136, can be
used to
hold a junction box connected to the PV cells 100. This allows for a finished
product that
?5 can be easily deployed and installed by affixing the module to the desired
location using
standard construction techniques, and simply connecting the junction boxes
either to
other modules or to a power conditioner/inverter. The structured module can be
easily
moved to the installation site, as it is durable, resistant to fracture, and
lighter weight than
a standard glass module of the equivalent size.
30 In another embodiment a complex corrugation pattern, similar to that used
in high
strength cardboard that can provide strength along both axes of the sheet is
used. Some
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of these complex designs require more advanced rolling techniques and
preferably
involve providing a wave pattern, such as herringbone, in the roll direction.
One feature of the corrugated designs, of the above described figures, is that
air
can flow directly against the back surface of the laminate. This provides
cooling to the
solar sheet, which is desirable to limit cell efficiency losses caused by
heating. In one
embodiment, the corrugate backing is preferably perforated, or even expanded
material,
which allows for the maximization of airflow while minimizing the weight of
the corrugate
with little detriment to structural integrity.
With corrugated designs, it is presently preferable to provide a nesting
feature with
a recessed junction box. This design allows two modules to be nested back-to-
back thus
minimizing shipment volume. Additionally, with the two sheet design of Figures
6 and 7,
the edges of the metal backed PV laminate 128 or the corrugate 126 can be
rolled over
the other, improving edge strength and protecting the installer from cuts.
An extruded three-dimensional sheet of material such as polypropylene or even
aluminum serving as a corrugate 126 behind the PV module 128 allows for
airflow 134,
though it may not offer the same cooling efficiencies as the air would not be
in direct
contact with the backing of the module and instead makes contact with the
metal layer.
In another embodiment, the PV prelaminate can be affixed to a rigid metal
backing
that forms the top layer of a sandwich. Two metal layers, one of which carries
the PV
module, can sandwich a polymer core such as polypropylene (PP) or polyethylene
(PE).
The end product is essentially a standard architectural product with
integrated energy
generating potential. After creating the PV module, grooves can be routed into
the back
surface of the product. By folding along the routed lines, the module can be
bent to form
three dimensional structures such as a frame around the perimeter of the
module.
The corrugated laminates of the present invention allow for a modular design
with
one or two junction boxes per module. The use of quick-connect cable
terminations
eliminates much of the on site wiring and assembly that some of the prior art
requires. As
a result, the product can be treated like a standard photovoltaic module for
installation.
As opposed to most of the prior art, no special installation training is
required, the module
is simply installed using standard photovoltaic module installation
techniques.
The corrugate construction provides a strong module that is both light weight
and
cost effective. In comparison to glass modules, the modules of the present
invention
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avoid increased weight per watt of generating capacity, as thicker corrugate
or thicker
superstrates are not required as the module size increases. Additionally, the
installation
is simplified as the modules are more robust and are not prone to shattering
if another
object impacts the module surface. The inclusion of the corrugate sufficiently
strengthens
the module so that it is as strong as conventional glass modules. In
comparison to prior
art systems employing flexible modules, the modules of the present invention
are
consistently rigid and do not have unsupported areas that cannot bear a load.
Additionally, the modular nature of the present invention avoids the prior art
problem of
requiring a specially trained installation crew, or requiring on-site module
assembly. This
reduces the installation costs and allows quality control to be exercised by
the
manufacturer. Assembly in a controlled environment is not possible with the
prior art
systems that require interconnected elements or provide the solar modules
separately
from the structural elements.
Figure 10 illustrates a the nesting of modules so that cells 100 face opposite
directions, and the corrugated sections of backing 126 nest within each other.
Junction
boxes 130 by being in one of the covered troughs do not interfere with the
nesting of the
modules. This allows for a smaller shipping volume to an installation site.
Figures 11 and 12 illustrate a solar module constructed to form standing
seams.
Whereas many prior art implementations are directed to affixing solar cells to
a standing
seam, the embodiment illustrated in Figure 11 has cells 100 spaced apart from
each
other, with a gap at fixed intervals. These gaps are folded into standing
seams 140 that
both increase the strength of the module, and raise the portions of the module
bearing
solar cells 100. By raising cells 100, seams 140 allow airflow under the
module and
provide a location for placing junction boxes and other such connectors. One
skilled in
the art will appreciate that the standing seam modules can also be nested,
although the
location of junction boxes will determine the orientation of the panels when
nested back to
back. This nesting allows for tighter packing in transit and a reduction in
the shipping
volume of the module. Figure 12 illustrates the encircled detail of Figure 11
and clearly
shows the placement of cells 100 with respect to seam 140.
One skilled in the art will appreciate that there are many ways that the
structured
modules of the present invention can be manufactured. One such method will now
be
discussed with relation to the flowchart of Figure 13. In step 150 a flexible
solar module
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is affixed to a metal backing. In the interests of reducing the mass of the
module it is
preferable to use a low density and strong metal such as aluminum. In addition
to
providing rigidity, the metal backing can serve as a heat sink to aid in the
dissipation of
heat buildup caused during the operation of the module. The flexible solar
module can be
attached to the metal backing in a number of ways including the use of a
fastener, an
adhesive, or the metal backing can be affixed by including the metal backing
in the
laminating process. It is preferable, though not required, that the module be
integral with
the backing, so that no folds or distortions occur later in the process.
In step 152, the metal backing is structured to allow for greater strength and
rigidity. This results in a module that has a rigid backing and a structure.
The structure of
the module provides strength, in at least one direction, and allows the module
to serve as
a replacement for conventional glass modules at lower cost and weight.
Figure 14 illustrates an embodiment of the above method, where the step of
structuring the metal backing is performed by corrugating the metal backing in
step 154.
In this embodiment of the method, it is preferable that the flexible solar
module is affixed
to the rigid backing in step 150 with spaces between cells to allow for the
corrugations.
Figure 15 illustrates a further embodiment, where the step of structuring in
step
152 includes attaching the rigid backed module to a corrugate in step 156. The
attaching
of the rigid module is preferably done by gluing, spot welding, or fastening
the rigid
backed module to the corrugate. In one embodiment, the edges of the corrugate
are
folded over the edges of the rigid backed module to strengthen the edges of
the product.
In other embodiments, the edges of the module are bent back to fold over the
edges of
the corrugate, or end caps are used to clamp the corrugate and the module
together.
End caps may be added to strengthen ends of the module and/or to control air
flow.
Figure 16 illustrates a further embodiment of the present invention, where the
rigid
backed module is bent to a structured form in step 158, as described above in
conjunction with Figures 8 and 9 or Figures 11 and 12. The rigid backed module
is
preferably bent to a structural form in step 158 and then secured to a frame
that provides
additional support and structure.
The above-described embodiments of the present invention are intended to be
examples only. Alterations, modifications and variations may be effected to
the particular
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CA 02567389 2006-11-20
WO 2005/119769 PCT/CA2005/000877
embodiments by those of skill in the art without departing from the scope of
the invention,
which is defined solely by the claims appended hereto.
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